Selective signal transmission system



Sept. 16, 1952 H. JANKOWSKI SELECTIVE SIGNAL TRANSMISSION SYSTEM Filed Aug. 1, 1951 Inventor Herman Jankowskl,

His ,Attovn ey- Patented Sept. 16, 1952 Herman Jankowski, Liverpool, N. Y,, assignor to General Electric Company, a corporation of New York 'Application-Au'gust'l, 1951, Serial- No. 2395823 6 Glaiimsn My f invention relates :in general to electrical transmission systems andin particular to transmission' systems'of the type forseleotively transmitting electrical signals between anyone of a plurality o'f x'pairsof terminals and a common pair 1 of terminals.

:An exemplary :a'pplicationin which the transmission system "of my :invention is. particularly advantageousgandin conjunction with which the invention will be describe'dxwithout intent of limitation thereto, is found in the magnetic storagesystems employed in computingiapp'aratus oi the" digital type. In these magnetic storage systemspnumbersand orders used inthe computing apparatusare storedrby recording .:plus. signals on -the magnetic surface of a revolving-drum. As the" drum revolves; a small section of its cylindrical r surfacezpassescontinuously under the pole tips-of each of a-i'plurality of magnetic recording and reproducing heads. Since there are a large number of recording and reproducing heads arranged :along the length of the drum, there is a problem in routing signals between any selected oneof the heads and a common circuit in recording'signals on orreceiving playback signals from any selected recording track along the drum. Since pulse information to be recorded on or played back from all of the tracks originates from or isrsentto-ra single-circuit, such as an amplifier,

in the computing'apparatus, it is desirable that it be possible for any onehead to be effectively connected individually for short'times to that single circuit for signal transmission therebetween. Further, it is desirable that signal transmission between the-signal circuit and the heads be switehedfrom one head to another with great rapidity and with a-minimum of switching transients in order to speed computing processes. And finally,r-because there are sometimesa great number of .such heads erge-moor more) to selectively receive signalsirom or send signals to the common circuit, it is desirable that the components and circuits for carrying out the selective'ac'tion'beisimple and economicalin nature.

It is an object of "my invention to provide a new and improved selective signal transmission system of "the'type described.

It'is afurther object of my invention to.provide such a transmissionsystem which is fast in "selective" action and which minimizes switching transients.

It'is a still further "objectoi 'fmyinv'ention to provide such-a transmission system that is made up of simple circuitry and economical components;

" Briefl'ystate'd,"my invention in one form there- 2 oi provides a-selective transmission system for transmitting signals between a commonfi-rstpair of terminals, such as the terminals of;an amplifier, and any one of a plurality of second pairs otterminals, such as the terminals of a. plurality of magnetic heads; A common tapped resistor, preferably centertapped by an adjustable connection, is connected inshunt relation withthe first pair of terminalswhilea plurality of'center; tapped resistors are also each-connected in-shunt relation with one of theseoondrpairs of termi-t nals. A'pair of similarly poled unidirectional imp'edances-are connected between the extremities of each of the-center tapped resistorsand the common tapped resistor. Whenadirect voltage of predetermined polarityl is applied between-the centertap ofthe resistor" in shunt with any selectedsecond pair of terminals and the tap -on the common resistor,eapositivebias is applied to the corresponding pair of unidirectional =impedances so that they presenttheir low -impedance characteristic :to the transfer of "signals between theselected second pair of terminals and the-common first pair of terminals, i; e.,the selected second pair of 'terminals is effectively connected to the firstcommonpair of terminals. for signal; -transmission' therebetween; However, whenthe applied direct voltage is reversed in pe'larity,-one-of the pair of unidirectional int-- pedances presents its "high impedance characteristic to the transmission of signalsand-efiectively disconnects the: selected second pair of terminals from-the common first pair, Thus, the switch= ing of any one of the second pairs of terminals into er fronrefiective; connection with the common iirst terminals is accomplished electrically, all physical connections being previously made,;, bythe :application of a biasing voltage in one. polarity or the other between the tap--of the common resistor and the tap of the resistor in; shunt with the onesecond pair of terminals, ;In a following .part of the specification -it will bev made apparent how-a positive bias voltage applied to allow signal transmission between one second pair of terminals and the common first pair of terminals may conveniently serve as the negative bias to prevent signal transmission between theremaining pairs of second-terminals andvthe first pair of terminals, and other opera tional advantages will be pointed out. v v

The-features of the present invention which LI. believe to-be novel are pointed out with particularity-in the appended claims. However,- for a' bet'ter'rundrstanding of the 'invention'both as to its organization and operation, andfor. further pbjects and advantages thereof, reference should be had to the following description taken in conjunction with the accompanying drawing, in which the single figure is a schematic circuit diagram of a selective signal transmission system embodying my invention and illustrated in connection with magnetic recording and reproducing heads.

Referring now to the drawing, I have shown a common first pair of terminals I and 2, which may be a part of a common input or output circuit such as a first winding 3 of a transformer 4, and which are to be selectively switched into eflective connection with one of a plurality of second pairs of terminals and 6, which in turn may be parts of separate output or input circuits such as signal coils I of magnetic recording or reproducing heads 8. While I have shown but three of the second pairs of terminals 5 and 6 and three of the heads 8 for illustrative simplicity, it will be understood that any number of these, similarly connected, may be employed to receive signals from or send signals to the common pair of terminals I and 2 as indicated by the free ends of the conductors in the lower portion of the drawing. Connected in shunt relation with terminals I and 2 and thus in shunt relation with the common circuit illustrated as first winding 3, there is a tapped resistor effectively constituted by a potentiometer II connected serially between a pair of equal resistors 9 and III, the series combination being connected in parallel across winding 3. By adjusting the movable tap I2 of potentiometer II to its midpoint, a preferred position, the equivalent of either two equal valued serially connected resistors or a center tapped resistor is formed. A plurality of center tapped resistors, effectively constituted by a plurality of pairs of equal valued resistors I3 and I 4 having a common junction or center tap l5, are each connected in shunt relation with one of the pairs of terminals 5 and 6, i. e., each connected in shunt relation with one of signal coils 1. A pair of unidirectional impedances I6 and. I1, preferably identical, is connected in series between each of the center tapped resistors I3-I4 and the tapped resistors 9II, each of impedances I6 thus connecting one of terminals 5, or one extremity of each center tapped resistor I3--I4, with terminal I, or one extremity of the tapped resistors 9Il; and each of impedances I! thus connecting one of terminals 6, or the other extremity of each of center tapped resistors I3I4, with terminal 2 or the other extremity of tapped resistors 9-H. All of the unidirectional impedances I B and I1 are similarly poled with respect to their corresponding terminals 5 and 6, i. e., oriented to present low impedance to conventional current flow in the same direction as shown in the drawing with respect to signal coils 1. Thus, unidirectional impedances I6 and I! may all be oriented to present low impedance to conventional current flow into coils I and high impedance to conventional current flow out of coils I; or as shown in the drawing, they may all be oriented to present low impedance to conventional current flow out of coils I and high impedance to conventional current flow into coils I. The movable tap I2, or center tap formed thereby if movable tap I2 is located centrally, of the series resistance combination 9II and the junction or center tap I5 of each pair of resistors I3-l4 are provided to receive a direct current biasing voltage therebetween, such a bias of one polarity or the other causing unidirectional impedances I6 and IT, to have either high or low impedance to signal transmission between a terminal pair 5 and 6 and the common terminal pair I and 2 and thus causing that pair of terminals 5 and 6 to be effectively disconnected or connected to the common terminals I and 2. Means for applying such biasing voltages may comprise fast acting, automatically controlled electronic circuits, or in the simplified illustrated form may comprise a voltage source illustrated as a battery I8 cooperating with a two-position switch I9. Positioning a switch I9 in contact with its bat tery I8 makes the junction or center tap I5 of the corresponding resistors I3 and I4 positive in polarity with respect to the tap or junction I2 of the common shunt-connected resistors 9-H.

A second position for switches I9 is shown for connecting the two taps directly, i. e., placing zero voltage between them, for a purpose to be explained presently.

It will be understood that magnetic heads 8 may be used either for recording intelligence signals on or reproducing intelligence signals from a moving magnetic recording medium such as a revolving drum. In the recording process,

therefore, heads 8 constitute a plurality of load' devices or output circuits, any one of which is to be selected at will to receive input signals from a common signal source or input circuit such as transformer 4. Conversely, in the reproduction process, heads 8 constitute a plurality of separate signal sources or input circuits any one of which is to be selected at will to supply signals to a common load device or output circuit such as transformer 4. The selective transmission system of my invention, as will be seen, is, therefore, a bilateral system and is not limited to the transmission of signals in only one direction. It will also become apparent that the signal voltage may be of either polarity or the sense of signal current flow may be in either direction.

For an explanation of the operation of the present transmission system, consider that it is de-' sired to transmit only signals reproduced in the signal coil 1 of the head 8 which is uppermost in the drawing to the primary winding 3 of transformer 4, remembering that all the while signal voltages are being simultaneously reproduced also in the signal coils 1 of the remaining heads 8 which are not to be transmitted to the common terminals I and 2. The uppermost switch I9 is positioned as shown in the drawing to be in contact with its battery I8, making the junction of the corresponding resistors I3 and I4 positive in potential with respect to tap I2 so that equal biasing currents flow, as shown by dashed I arrows, through the unidirectional impedances I 6 and I1, hence in opposite directions through resistors I3 and I 4 and through resistors 9 and I 0 producing voltage drops across the resistor pairs which cancel and cause little or no resultant voltage drop across the shunt-connected resistor combinations.

The purpose of potentiometer II is now apparent, that purpose being to allow for slight adjustments compensating for minor inequalities in the forward resistances of unidirectional impedances I6 and I1 and in the two halves of the center tapped resistors, which from a practical viewpoint are apt to exist. A similar potentiometer may be provided between resistors l3 and I4 if it is desired. The desired setting of movable tap I2, then, is that setting for which the total ing currents are not exactly equal because of slight'iinequaiitiesiin atheiiorward resistazices f; impedances lfi an'difl; iImmosmcasessthessettina reverse resistance to: currentifl'owin the-opposite:

direction; 'I'he impedances may be 'ofzlanyetype vacuum-diodes, :contact. rectifiers; orzicrystalafdi cdes-+the latter -having zzbeenil'found completely, satisfactory. .Oneireadily obtainable type :of :crysa tali diode;iforaexample,:haszza'forwardsresistarice of "about 250 I ohmsxibut ;-a;.ireverse resistanceiflof. about 1v imillion ohms: Thezmagnitudesirof the, voltageiof battery I9: is ChOSBIIJSllCh' thalt iihelfbrrz' ward s biasing current through qe'achzzofr the:;:im-. petla'nces: l6 Land. 1 I i is atgleast ::as, .great as the maximum signallcurrent' :to :be transmitted he:

tween 'ak pair or. terminalsiiand. 6 fiandz-terminals;

I rand I12 1 this insuring :that-r'at iiall times 2 during. signaltransmissio .both of impedances l6 :anda. l 7 are t. conducting :currentiin a :rforward direction and'have'lowmesistance tothetra-nsie'r ofzsignals.

Stated :another way,.":transmitted i-signal current mayv be thought :of-as: modulating x-the direct: bi-a asing current but never tozsuchaanxextent sthat. theitotalzcmrent tends toriflow ina reverse-directionzthrcughiimpedancesa l 6- or l I. The -magni tuelesz'of the. resistors, in turn, are :chosen to be suflicientlyzhighaso; that appreciablewshunting of the, signalxcurrent :does not result;- Thusxif a voltageipulse, for example, is reproduced-in signal coil 1 of the upper ahead =8, .yit .-is transmitted through".thecorrespondingimpedances: l 6 and j 1, increasing the total current in one'and decrease ingthe. total current in the'other, but not: to-the extent that current .'.tends ,to. flow ina-a :reverse direction:therethroushytof .the :transformer winde ingu3 :withvery little:attenuation;

Consider :next the remaining two lower; heads 8 in .thedrawing which. are -to; be -reffectiv1elywdis connectediromwvindin'g' 3 so' tha-t: only signals fromthe upper head-'18. are transmitted-to :winding 3. If a reverse voltage .bias, i.-:e. *adirect r-yoltage tending to I cause currentvin therhigh resistance 1 direction, is ;placed on ;the..- lower spair. of impedances I 6 and I I; only-a veryrsmall, negligible biasing :current can flow and -a=.large- ;reverse. voltage drop. appears,- in .the ;polarity shown; across the lower pairs of impedances ltiand -tlz The magnitude 'ofithe' reverse biasing voltage is chosen to be at least as great as the maximum signal voltageitoberreproduced in'coils 1, so that under-these conditions, Vbothimpedancess'lc and I? always'have a reverse polarity voltage-drop across them and present their highreverse resistances, thereby'to cause great attenuation of the signal voltages inducedrincoil I anclaefiectively .prevent the .transmissiQnao-f 'suchj-Esignal voltagesgto winding ..3..

In accordance with.,.an. important aspectfio'f my invention, the use of a separate reverse biasing voltage source is not necessary as shown in conjunction with the lower two heads 8 in the drawing. The lower two switches [9 are positioned to directly connect the center tap l5 of the lower resistance l3l4 to the tap [2 whereby the voltage drops appearing across the two halves of the resistance 9ll as a result of the upper battery l8 are applied to the lower impedances ;lfiiandi'lfliasireuersexbiaswoltagesrmar 17011171185 o'ltageszdividingiaction'iof:the upperere-a sisters; 3 lltean'd vl lathisrrex ersezbiae :onatheiower it'll-2 pedances t6 :and- 1| 11isz=inrmagnitude som'e 'frac Sand: t4randtithericommon resistors bidni fifi the itotal voltage rorathe jrupper battery l'8'a However;tthewdltagecof: batteryi l 8' maynbe chosen soithat thelreverse :bias -:on :each. of Time loweriimpedancesi1.6 and; l Ii-is; at leastsasigreat as lthe :LmaXimum signalirvoltage I toibe lnduced' in th'eiioweresignahcoil 1;;so .that'ilthelattenuat ing action effectively disconnecting the lowerstwo coils ZL'IIJII Om :winding 1, 3 :is :obtained; .'Ihus, the

' preferredsiformionmy inventiomrequires:nofisep aralte rreverse; biasingssou'rces =ra1though lzit rwill= be understood v.by. I-Lthose skilled? in the 1 art that;

suclriseparate sources mayibe employedrwithi'vmy inventionvwithout departingztherefrom.

. In ritheailight: of ith'e foregoing descriptiomi it''- becomes ievidentiithati the switching :system 201' my; invention :iprovidestiorithe .aselective 't;transmissioniofrsignalsibetweemany selectedionelof a pluralityzoi'tpairseofiterminalsiand a pair of come mon -terminals by'ithe .application of r'axdirect biasing qvolta'ge Cof predetermined 'polarity ito a biasing .circuitiassociated withlthei:sele'cted"pair of terminals,- -.thei'remainings;ones :of -:th'ei-- plurality of pairs f fte'rminals abeing iiefiectively dis-:-

connected: from the :commompair ofziterminals' by the negative biasingcaction of the applied direct voltage. It will ialsozibefapparentl'thattheiorientation :of all of ithe unidirectional im-. pedances is: and l l 1 'l'may .equa-lly well :-:be 4 onpositeto -tha'tishown in the-drawing, "the polarity.

of the biasing source battery l8ribeing, made core respondingly opposite-to that shown. Thelpresent' "transmission "system :is' very fast actingrin:

switching .lfrom one selected pair of :zjterminals to anothergm'a'king .possible the switching from; one'iset ofziterminals' 5,5- to :another in :thesor-dcr:

of 1'00 1' microseconds i in aconstructed embodi ment by usingvelectronic circuits to.:provide;the

direct -biasing voltages. Transient current cflowcaused by switching from :one pair of'terminals: 5-'-'-6 to another, e., lremov-ingfthe' biasing i volt tageforione pairiofite'rmina-ls i5-'6 and applying a ::biasing J voltage fori'anotherris rminimized .r.by= the'fact 'that't-the voltage across 11311.8"Shl1lltf00111 nected resistor: combinations due to biasin cur rent may:besadjustedttobe:zero; so;that if the signal-voltage :isrzeroiat thetime of: switching, asitymost' always isin practice, the-circuitsconnected $011118. common-terminals ir'andi2 ands tolxthe pairs of i.terminals:5ri6#"aregenerally:dew-

energizedcandzonly very short duration: andfilow.

amplitudevrtransients"Iesulti v v While cathe ipresent f'i invention: has. been: de

scribed-byirreference'. to asparticular: embodiment r thereof; itkwill be; understood that "modifications: mayzbe. made by'thoserskilledzin thecartiwithouttactually departing from the invention. 7 I; therefore, ;aim.in the appended claims: to; .-:coverall :such equivalent :;variations: as srcome "within the ctrue SDllitlrflhdfiSCOPG;iOf ,the pioregoingadi'srclosure.

second pairs of terminals, and a plurality'of pairs 01' unidirectional impedances each similarly poled and connectingthe extremities of each of said center tappedresistors-and the extremities of said tapped resistor, whereby a direct voltage of predeterminal polarity applied between the tap of said tapped resistor and the center tap of any one of said center tapped resistors efiectively connects only the corresponding second pair of terminals to said first pair of terminals for signal transmission therebetween.

2. Av selective signal transmission system for selectively transmitting electrical signals between a first pair of. terminals and any one of a plurality of second pairs of terminals, said system comprising a first center tapped resistor connected in shunt relation with said first pair 01' terminals, a plurality of other center tapped resistors each connected in shunt relation with one of said second pairs of terminals, and a pair of unidirectional impedances connected with like polarity between the extremities of each of said other center tapped resistors and the extremities of said first center tapped resistor, means for removably connecting the center tap of each of said other resistors to the center tap of said first resistor, and means for removably applying a direct voltage of predetermined polarity individually between the center tap of one said other resistors and the center tap of said first resistor whereby the correspondingone second pair of terminals is effectively connected to said first pair of terminals for signal transmission therebetween.

3. A selective signal transmission system comprising a plurality of signal sources, a plurality of center tapped resistors each connected in parallel combination with one of said sources, an output circuit, a center tapped output resistor connected in parallel combination with said output circuit, a pair of similarly poled unidirectional impedances in series with each of said signal sources and said output/circuit, a direct voltage source of predetermined polarity being connected between said output resistor center tap and the center tap of any one of said plurality of center tapped resisters for transmission of signals from the corresponding one source to said output circuit.

4. A selective signal transmission system for selectively transmitting electrical signals from a single signal source to any one of a plurality of load devices, said system comprisin a first pair of serially-connectedresistors connected in shunt relation with said signal source, a plurality of second pairs of serially-connected resistors each connected in shunt relation with one of said load devices, and a pair of unidirectional impedance devices connected with like polarity between the extremities of each of said second pairs of serially-connected resistors and the extremities of said first pair of serially-connected resistor, whereby a direct voltage of predetermined polarity applied between the junction of any selected one of said second pairs of resistors and the junction of said first pair of resistors efiectively connectsonly the load device corresponding to said. selected one second pair of resistors for receiving signals from said source.

5. A'selective signal transmission system for selectively transmitting electrical signals between a first pair of terminals and any one of a plurality of second pairs of terminals in response to electrical actuation; said system comprising a first resistor, a potentiometer having an adjust able tap, and a second resistor in series combination in the order named connected in shunt relation with said first pair of terminals; a plurality of pair of equal valued serially-connected resistors each connected in shunt relation with one of said second pairs of terminals; a pair of substantially identical unidirectional impedances each serially connected with like polarity between said first pair of terminal and one of said second pairs of terminals; whereby a direct voltage of predetermined polarity applied between said adjustable tap and the junction of a selected one of said pair of resistors biases the pair of unidirectional impedance devices associated with said selected pair of resistors to effectively connect the second pair of terminals associated with said selected pair of resistors to said common pair of terminals for signal transmission therebetween,

and biases the remaining pairs of said unidirec-.

tional impedances to effectively disconnect the remaining second pairs of terminals from said first pair of terminals.

6. Thecombination of a transformer and a plurality of magnetic recording and reproducing heads with a selective signal transmission system for selectively transmitting electrical signals between any one of said heads and said trans former, said transformer having an electrical Winding, said recording heads each having a signal coil, said transmission system comprising a first center tapped resistor connected in shunt relation with said first winding, a plurality of cener tapped resistors each connected in shunt relation with one of said signal coils, a pair of unidirectional impedances oriented with like polarity connecting the extremities of each of said second resistors with the extremiies of said first resistor, and means for individually applying a direct voltage of predetermined polarity between the center tap of any one of said second resistors 1 and the center tap of said first resistor whereby the corresponding one signal coil is effectively connected to said electrical winding for signal transmission therebetween and the remaining signal coils are effectively disconnected from said electrical winding.

' HERMAN JANKOWSKI.

REFERENCES CITED The following references are of record in the file of this patent:

. UNITED STATES PATENTS Number Name Date 2,561,051 Hertog July 17, 1951 2,563,589 Hertog Aug. 7, 1951 2,583,711 Scowen Jan. 28, 1952 

